1. Technical Field
This disclosure relates to an image forming apparatus such as copiers, printers, facsimiles or their complex machines, and more particularly to an image forming apparatus equipped with a protectant applicator applying a protectant to an image bearer to protect the image bearer from mechanical stress such as friction with a cleaning blade and from electrical stress when charged. In addition, this disclosure relates to the protectant applicator and a process cartridge or use in the image forming apparatus.
2. Description of Related Art
In an electrophotographic image forming apparatus, an image bearer such as a photoconductive photoreceptors is subjected to a charging process, an irradiating process, a developing process and transferring process to form an image. Discharge products produced in the charging process, remaining on the surface of the photoreceptor and residual toners or toner components remaining thereon after the transferring process are removed in a cleaning process.
Conventional cleaning methods use an inexpensive and simple cleaning blade formed of a rubber or urethane, having good clean ability. However, since the cleaning blade is pressed to the surface of a photoreceptor to remove residues thereon, a stress due to friction between the surface of a photoreceptor and the cleaning blade is large and the cleaning blade and the photoreceptor, particularly an organic photoreceptor, are abraded, resulting in shorter lives thereof.
In addition, a toner used for forming images is having a smaller particle diameter to produce higher quality images. The smaller the particle diameter, the more the toner scrapes through a cleaning blade. Particularly when the cleaning blade has insufficient dimensional accuracy, assemble accuracy or partially oscillates, the toner scrapes through the blade more, resulting in production of poor quality images.
So as to extend the life of an organic photoreceptor to produce high quality images for long periods, deterioration of members such as a cleaning blade due to abrasion needs to be reduced to improve clean ability thereof.
Practically, a lubricant is applied to the surface of a photoreceptor with a cleaning blade to form a film of the lubricant on the surface of the photoreceptor. The lubricant applied to the surface of a photoreceptor reduces abrasion of the photoreceptor due to friction between the cleaning blade and the photoreceptor and deterioration thereof due to discharge energy when charged. In addition, the lubricant increases the lubricity of the surface of a photoreceptor, and reduces partial oscillation of the cleaning blade and the number of toner scraping through the blade. However, since the insufficient lubricant does not exert sufficient effect of lubricity and surface protectivity against the abrasion of a photoreceptor, deterioration thereof when charged with an AC voltage and scraping through the blade of a toner, an image forming apparatus in which an amount of a lubricant applied to the blade is specified is disclosed.
For example, Japanese published unexamined applications Nos. 2005-17469, 2005-249901, 2005-004051 and 2004-298662 disclose an image forming apparatus in which an amount of zinc stearate applied to the surface of a photoreceptor is specified with a ratio of a zinc element to total elements detected by a XPS (X-ray photoelectron spectrometer) analysis on the surface of the photoreceptor. XPS detects all elements except for hydrogen on the surface of a sample. When the surface of an organic photoreceptor coated with zinc stearate (C36H70O4Zn) by XPS, as the coverage of the zinc stearate increases, the element ratio the organic photoreceptor has closes to that of the zinc stearate. When the coverage of the zinc stearate becomes 100%, the element ratio theoretically coincides with that of the zinc stearate and the detected amount of zinc is saturated. Namely, when the zinc stearate covers the whole surface of a photoreceptor, from the element ratio except for hydrogen in a molecule of the zinc stearate, the zinc element ratio is theoretically 2.44% to that of all the elements detected by XPS.
Japanese published unexamined application No. 2004-298662 discloses specifying an applied amount of the protectant by XRF (X-ray Fluorescence) to produce high quality images for long periods. However, depending on the way of using 3 the image forming apparatus, images having parts having uneven image density or abnormality are frequently produced.
Because of these reasons, a need exists for an image forming apparatus capable of well providing and applying a protectant to its image bearer to prevent production of abnormal images and produce high quality images for long periods.